1. Field of the Invention
The present invention relates to an impurity-doped semiconductor material with a BC (bond-center) structure and a method of producing the same, and further relates to a light emitting device and a light receiving device.
2. Description of the Related Art
In recent years, studies regarding the band engineering intended to modulate the unique optical characteristics of a substance, such as light emission and absorption, by modulating the energy band structure having been considered as being inherent to the substance are being activated.
For example, a quantum dot (quantum wire or very thin film) is well known as a representative band engineering method. The quantum dot (quantum wire or very thin film) provides a method of reducing the size of a substance three-dimensionally (two-dimensionally or one-dimensionally) so as to confine electrons therein, thereby modulating the band structure thereof.
On the other hand, a bond stretching effect can be mentioned as providing a band engineering method in which the band structure of a semiconductor is modulated by a principle entirely different from the above. The bond stretching effect provides a method of applying a stretching stress to a substance so as to attain bond stretching, thereby modulating the band structure thereof.
FIG. 1 shows the pressure dependence of each of three energy gaps of Γc-Γv (direct transition), Lc-Γv (indirect transition) and 0.84Xc-Γv (indirect transition) with respect to silicon (see K. J. Chang et al., Solid State Commun. 50, 105 (1984)). The extrapolation lines shown in the figure are those calculated from the pressure coefficients appearing in the literature. The pressure coefficients of (Γc-Γv), (Lc-Γv) and (0.84Xc-Γv) are 11.6 meV/kbar, 3.8 meV/kbar and −1.6 meV/kbar, respectively.
The extrapolation lines of FIG. 1 suggest that, in a tensile pressure region, the band structure of silicon changes to the direct transition. In essence, the bottom of conduction band shifts from 0.84Xc to Γc under the tensile pressure. This result clearly suggests that, if the Si—Si bond can be stretched, the band structure of silicon can be converted to the direct transition as in compound semiconductors represented by GaAs.
However, no method of applying an external tensile pressure of several hundreds of kilobars in order to attain a bond stretching is known. Therefore, there is no example of success in the conversion of silicon to the direct transition by the bond stretching effect. In short, there is the problem that the conversion to the direct transition by the bond stretching effect is in no way a practical method.
The indirect semiconductors, including silicon, are essentially nonluminescent and exhibit weak absorption. Accordingly, up to now, it has been in principle difficult to fabricate a light emitting device based on an indirect semiconductor. Although a light receiving device based on an indirect semiconductor has been fabricated, due to a low absorption coefficient thereof, its photosensitivity and response speed have had a trade-off relationship. Namely, there has been the problem that when a thick-film device is employed for higher photosensitivity, a decrease of response speed would be invited, and that contrarily when a thin-film device is employed for higher response speed, a decrease of photosensitivity would be invited.
In summing up, the bond stretching effect would provide a novel band engineering method permitting the conversion of silicon to the direct transition, and the application thereof to the indirect semiconductors, including silicon, would work to bring about novel optical functions, such as strong luminescence and high absorption. However, there is the problem that no practical method of applying to silicon a tensile pressure on the order of several hundreds of kilobars required for the conversion to the direct transition is known.